Hydraulic assistance device

Abstract

Hydraulic assistance device of the mixed hydrodynamic/hydrostatic type incorporating a body (10) in which a first piston (18) is slideably mounted and moveable between a first position allowing the communication of a first chamber (53), joined to a braking circuit, to a reservoir (12), and isolating this chamber (53) from a source of high pressure fluid (86), and a second position isolating the chamber (53) from the reservoir (12) and connecting it with the source (86); a second chamber (30) in the body (10) connected by a passage (90) to the brakes (66), and valve mechanism (92) normally closing the passage (90) and sensitive to the pressure in the chamber (30) so that, when the latter pressure reaches a value which is greater than that existing in the first chamber (53), the valve mechanism (92) opens allowing fluid to flow between the second chamber (30) and the brakes (66).

I claim: 
     
       1. A hydraulic assistance device incorporating a body provided with a bore in which a first piston is slideably mounted and movable by actuation of a brake pedal, between a first position allowing communication of a first chamber joined to a braking circuit and a low pressure reservoir, and isolating the first chamber from a high pressure source, and a second position isolating the first chamber from the low pressure reservoir and placing the first chamber into communication with the high pressure source, the device including a second chamber formed in the body and a first passage communicating the second chamber with the brakes, characterized in that the device comprises first valve means in the first passage so that the first passage is normally closed, the first valve means being sensitive to pressure in the second chamber so that when pressure in the second chamber exceeds pressure existing in the first chamber the first valve means opens to allow fluid to flow between the second chamber and brakes, the first chamber formed in the bore between the body and a sleeve, the communication between the first chamber and reservoir including a second bore in the sleeve, a second piston slidably mounted in the second bore and connected with the first piston, second valve means between the high pressure source and first chamber and capable of being controlled by the second piston, an annular space in the bore between the sleeve and the body, the first valve means including a lipped annular seal mounted on the sleeve, a push rod slidably mounted in a bore in the first piston and joining the first piston to the second piston, the communication between the first chamber and reservoir including a bore in the second piston, a second passage in the push rod and an opening in the first piston, and third valve means controlling the communication between the first chamber and reservoir. 
     
     
       2. The hydraulic assistance device in accordance with claim 1, characterized in that the push rod further comprises fourth valve means linked to the third valve means and operable to close the communication between the first chamber and reservoir. 
     
     
       3. The hydraulic assistance device in accordance with claim 2, characterized in that the device further comprises spring means operable to urge the fourth valve means into a closed position. 
     
     
       4. The hydraulic assistance device in accordance with claim 3, characterized in that the fourth valve means is located in the second passage in the push rod. 
     
     
       5. The hydraulic assistance device in accordance with claim 4, characterized in that the device further comprises a pin slidably mounted in the second passage and linking the fourth valve means to the third valve means.